JPS61197205A - Orientation blow molding preform - Google Patents

Abstract

PURPOSE:To contrive an improvement in workability and gas barrier properties of blow molding, by a method wherein the titled preform is an article formed of polyester and gas barrier thermoplastic resin, whose intermediate layer is thin at the bottom and is made thick extending from the lower part of a body to the upper part of the same. CONSTITUTION:As for an intermediate layer 12, it has thickness distribution structure wherein it is most thin at a central part 14 of the bottom, the more it goes upward from the lower part of a body the thicker a thickness is increased and the thickness becomes maximum at the top part 13. As for a grade of the thickness distribution, when the thickness of the center 14 of the bottom of the intermediate layer and that of the top 13 of the intermediate layer are made into t2 and T1 respectively, t1/t2 is given an 1.1-25. At the time of orientation molding of a preform, as for the intermediate layer 12, favorable orientation molding operation is performed at the tip art 13 of a thick part of the same without generating a deviation of a position and a slip between an inner and outer polyester surface layers 10, 11.

Description

[Detailed description of the invention] Industrial application field The present invention is a stretch blow molding preform (preformed product)
More specifically, the present invention relates to a preform that enables the production of a multilayer plastic container that is excellent in stretch blow molding workability, and has excellent gas barrier properties and molecular orientation effects.

PRIOR ART AND TECHNICAL PROBLEMS OF THE INVENTION Polyester containers made by stretch blow molding have excellent transparency and appropriate rigidity, and can be used not only for liquid detergents, shampoos, cosmetics, soy sauce, sauces, etc., but also for beer, cola, and cider. It has come to be widely used in containers for soft drinks such as carbonated drinks, fruit juices, and mineral water.

Although this stretched polyester container has superior gas barrier properties compared to general-purpose resin containers such as polyethylene and polypropylene, it is negligible compared to cans and bottles, which have almost zero gas permeability. It has low permeability to oxygen and carbon dioxide, and the shelf life of its contents is limited to a relatively short period.

In order to improve this drawback, various proposals have been made to improve the gas barrier properties of containers by combining polyester with gas barrier resins such as ethylene-vinyl alcohol copolymers to create a multilayer structure. .

To manufacture a stretched multilayer plastic container, it is first necessary to manufacture a multilayer preform, and various methods such as coextrusion, multistage injection molding, coinjection molding, etc. are used to manufacture this multilayer preform. method is used.

However, when actually stretch blow molding these multilayer preforms, an obstacle is encountered in that the ethylene-vinyl alcohol copolymer has extremely poor stretching workability compared to polyester.

That is, it is known that when an ethylene-vinyl alcohol copolymer is stretched in the form of a single layer, it breaks under normal forming conditions (Japanese Patent Publication No. 57-4249).
(See Publication No. 5). In particular, when stretch-molding a laminate of oriented resin and ethylene vinyl alcohol copolymer,
It is said that when the adhesion between both resin layers is insufficient, defects such as breaks and cracks are likely to occur in the copolymer layer.
Fact 1: Since there is almost no thermal adhesion between the ethylene-vinyl alcohol copolymer and polyester, we believe that it is necessary to interpose a special adhesive resin layer between the two resin layers. Since then, many efforts have been made to search for adhesive resins.

Summary of the Invention The present inventors have manufactured a preform for stretch blow molding comprising inner and outer layers of oriented, creep-resistant resin such as thermoplastic polyester and a gas barrier intermediate layer such as ethylene-vinyl alcohol copolymer. In this case, when the intermediate layer is completely enclosed between the inner and outer layers by co-injection, and the thickness of the intermediate layer in the portion reaching above the cylindrical body is made thicker than the thickness of the intermediate layer at the bottom, The workability of the preform stretching process has been significantly improved, and this has led to the improvement of gas barrier
It has been found that effective molecular orientation can be imparted to both the inner and outer creep-resistant resin layers and the gas barrier intermediate layer without causing problems such as breakage and cracks in the intermediate layer.

The present inventors have further discovered the surprising fact that the above advantages are possible even when no special adhesive is provided between the creep-resistant resin inner and outer layers and the gas barrier intermediate layer.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a preform for stretch blow molding that enables the production of multilayer containers that have excellent workability in stretch blow molding and also have excellent gas barrier properties and molecular orientation effects. be.

Another object of the present invention is to provide a stretch-blow film comprising polyester inner and outer surface layers and an ethylene-vinyl alcohol copolymer intermediate layer, which enables molecular orientation by stretching both resin layers without the need for special adhesives. To provide molding preforms.

According to the present invention, there is provided a stretch blow molding preform comprising a mouth portion, a cylindrical body portion and a closed bottom portion formed from a multilayer plastic, the preform comprising an inner and outer layer of an oriented, creep-resistant resin. Consisting of a surface layer and an intermediate layer of gas barrier thermoplastic resin completely encapsulated between the polyester layers, the intermediate layer is thinnest at the bottom and increases in thickness from the bottom of the body to the top of the body. The thickness of the middle layer above the trunk (t1) is the thickness of the bottom middle layer (t1).
A preform is provided having a thickness of 1.1 to 25 times t1).

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In the following explanation, thermoplastic polyester is cited as a typical example of the creep-resistant resin, and ethylene-vinyl alcohol copolymer is cited as a typical example of the gas barrier resin, but the present invention is not limited to these combinations. Not done.

Preform Structure, Functions and Effects In FIG. 1 showing the preform of the present invention, the preform 1 consists of a mouth portion (nozzle portion) 2, a body portion 3 and a closed bottom portion 4. As shown in FIG. The mouth part 2 has a shape and dimensions corresponding to the mouth part of the final stretch-blow-molded container, and is provided with a thread 5 for fastening the lid and a support ring 6 for supporting the container during filling and sealing. . The outer circumferential surface 7 of the trunk 3 from just below the mouth is a circumferential surface with a substantially constant outer diameter, but on the inner surface side of the trunk there is a chino surface 8 whose inner diameter gradually decreases from just below the mouth. , below this Chinow surface 8 is a circumferential inner surface 9 having a substantially constant inner diameter.

In this way, by gradually increasing the thickness of the body 3 from just below the mouth, stretching from just below the mouth can be effectively performed during stretch blow molding.

This preform has an inner surface layer 1 made of bori ester.
0 and an outer surface layer 11, and an intermediate layer 12 of ethylene-vinyl alcohol copolymer completely encapsulated therebetween. That is, this intermediate layer 12 exists as an intermediate layer over the entire surface of the closed bottom part 4 and the body part 3 without being exposed to the surface in any part of the preform. Although it does not exist at the upper end of the mouth part 2 of this intermediate layer 12, the intermediate layer tip 1 is located at least above directly below the mouth part.
3 exists.

The preform of the present invention has several features not found in conventional multilayer freeforms.

That is, as is clear from the cross-sectional view in FIG. It has a partial structure with a thickness of . The gradient of this thickness distribution is such that the thickness at the bottom center 14 of the intermediate layer is 'c tz and the thickness at the top end 13 of the intermediate layer is 1. It is expressed as a ratio of tl/12. In the preform of the present invention, the gradient of the distribution of the intermediate layer thickness (t s/l
*) is generally in the range from 1.1 to 25, in particular from 1.5 to 20.

According to the present invention, by providing such a thickness distribution to the ethylene-vinyl alcohol copolymer interlayer, significant advantages are achieved in terms of workability in stretch blow molding, and furthermore, the final multilayer Extremely significant advantages are also achieved in terms of gas barrier properties and molecular orientation effects of plastic containers.

Stretch blow molding of a bottomed preform involves pressing an arc stretching rod against the inner surface of the bottom of the preform, pulling and stretching the preform in the axial direction, and blowing fluid into the inside of the preform to expand and stretch it in the circumferential direction. This is done by In the preform of the present invention, the upper end 13 of the ethylene vinyl alcohol copolymer intermediate layer is significantly thicker than other parts;
The intermediate layer in the preform forms a cross-section of the model as a whole. Because of this feature, during stretch forming of a 7-ohm grid, the intermediate layer 12 is firmly held at its thick tip 13 between the inner and outer surface layers 10 and 11 of the varnish, and as a result, the position of the intermediate layer 12 does not shift. , a good stretch forming operation can be carried out without causing any slippage.

As already mentioned, the ethylene vinyl alcohol copolymer is a resin that has inferior stretch molding performance compared to polyester and the like. In addition, there is almost no adhesion between the ethylene-vinyl alcohol copolymer and the flash ester, and in the conventional stretch molding method, when there is no strong adhesion between the two, the ethylene-vinyl alcohol copolymer It has already been pointed out that the copolymer layer is prone to breakage and cracks.

In contrast, according to the invention, even if no adhesion takes place between the intermediate layer 12 and the inner and outer surface layers 10.11, the mechanical bond between the intermediate layer 12 and the inner and outer surface layers 10.11 Since the target alignment is closely maintained throughout the entire stretch-forming process, it is possible to perform molding at a high stretch ratio without causing any defects such as breaks, cracks, or pinholes in the intermediate layer 12. This was completely unexpected based on the conventional wisdom mentioned above.

Moreover, according to the present invention, the ethylene-vinyl alcohol copolymer can also be effectively stretched together with the inner and outer polyester layers due to improved stretch-molding workability, making it possible to orient the molecules in the plane direction. Due to this molecular orientation, the gas barrier of the ethylene-vinyl alcohol copolymer is significantly improved; for example, the gas permeability coefficient (Po1) for oxygen is as small as two-thirds to one-fifth of that of non-oriented copolymer. Become.

Furthermore, in stretch blow molding of a preform with a bottom, the stretch ratio differs significantly depending on the preform, and therefore each part of the container. Generally, the stretch ratio is highest at the shoulders; for example, when the average area stretch ratio is 4 times, the area stretch ratio at the shoulders reaches 8 to 10 times. Thus, although there is an effect of improving gas barrier properties at the shoulder of the container due to molecular orientation, the gas permeation of the container as a whole decreases as a result of the decrease in the thickness of the container wall and therefore the thickness of the gas barrier intermediate layer. This results in a disadvantage.

In the present invention, the bottom intermediate layer with the smallest draw ratio is made the thinnest wall, and the wall thickness increases toward the upper part of the body (the part corresponding to the container shoulder) where the draw ratio is the highest. This makes it possible to compensate for the decrease in the thickness of the intermediate layer and improve the gas barrier properties of the entire container.

The stretch blow molding preform of the present invention has several additional features not found in conventional preforms of this type, also in connection with freezing, which will be described later. One of them is that the ethylene-vinyl alcohol copolymer intermediate layer 12 is thinner than the polyester outer surface layer 10.11, and the center plane 15 (dotted chain a) of the vessel wall cross section is also biased toward the inner surface. As described in detail later, this makes it possible to manufacture a stretch blow-molded container with excellent pressure resistance and impact resistance. The second is the inner and outer surface layer 10.11
and the intermediate layer 12 have a low peel strength of less than 200 g/L 5 m width when the preform body 3 is cut in the thickness direction. It shows no tendency to delaminate either when subjected to molding or in the form of the final container.

Material In the present invention, polyethylene terephthalate (PET) is suitably used as the thermoplastic polyester, but copolyesters mainly composed of ethylene terephthalate units and containing other polyester units may be used as long as the essence of polyethylene terephthalate is not impaired. may also be used. Copolymerization components for forming such a copolyester include isophthalic acid, P-β-oxyethoxybenzoic acid, naphthalene 2,6-dicarboxylic acid, diphenoxyethane-4,
Dicarboxylic acid components such as 4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sepacic acid or their lanoalkyl ester derivatives, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene Glycol components such as glycol, cyclohexane dimetatool, ethylene oxide adduct of bisphenol A, diethylene glycol, and triethylene glycol can be mentioned.

The thermoplastic polyester used preferably has an intrinsic viscosity (n) of 0.5 or more, especially KO, 6 or more from the viewpoint of the mechanical properties of the vessel wall. Furthermore, this polyester can also contain additives such as coloring agents such as pigments and dyes, ultraviolet absorbers, and antistatic agents.

Other examples of oriented, creep-resistant resins include polycarbonate, polyarylate, polysulfone, polyether sulfone, polyphenylene oxide, ? Riphenylene sulfide, polyetheretherketone, Po+J
-4-methyl-4-ten-1, polypropylene, impact-resistant polystyrene, polymethyl methacrylate, acrylonitrile/styrene copolymer, polyvinyl chloride, and the like.

In the present invention, the gas barrier resin layer has a vinyl alcohol content of 40 to 85 mol%, 50 to 85 mol%.
It is important to use an ethylene-vinyl alcohol copolymer of between 80 and 80 moles.

In other words, ethylene-vinyl alcohol copolymer is the resin with the best sparring properties, and its sparring properties and thermoformability depend on the vinyl alcohol unit content. When the vinyl alcohol content is as low as 40 moles, the permeability to oxygen and carbon dioxide gas is greater than when it is within the above range, and it is not suitable for the purpose of the present invention, which is to improve gas barrier properties. On the other hand, if the content exceeds 85 molt, the permeability to water vapor increases and the melt moldability decreases, which is not suitable for the purpose of the present invention.

The ethylene-vinyl alcohol copolymer is obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl acetate so that the degree of saponification is 96% or more, particularly 99% or more, In addition to the above-mentioned components, this copolymer may contain 3-carbon atoms such as propylene) butylene-1, imbutylene, etc., within a range that does not impair the barrier properties against oxygen, carbon dioxide, etc., for example, within a range of up to 3 mol. The above olefin may be contained as a comonomer component.

The molecular weight of the ethylene-vinyl alcohol copolymer is not particularly limited as long as it has a molecular weight sufficient to form a film, but it is generally used at a temperature of 30°C in a mixed solvent of 85% by weight of phenol and 15% by weight of water. The intrinsic viscosity [n
] is preferably in the range of 0.07 to 0.17M&.

Other examples of gas barrier resins include aliphatic polyamides, aromatic polyamides, unsaturated nitrile resins, polyvinylidene chloride, and sparring polyesters.

In the following examples, polyester is used as a representative resin having orientation resistance and creep resistance, and ethylene-vinyl alcohol copolymer is used as a representative example of a f-sparing resin.

In the present invention, as will be described in detail later, forming a clearly differentiated layered flow of polyester and ethylene-vinyl alcohol copolymer within the cavity of the injection mold improves the gas barrier properties of the container. It is important in this point. For this purpose, the difference in structural viscosity index is 0.01 as ester and hyethylene-vinyl alcohol copolymer.
Preference is given to using combinations within the range 1o to 1o, especially 0505 to 5.

In this specification, the structural viscosity index and the melting point of the higher one of both resins are also 5°C higher for 100 s.
This is the value obtained from the flow curve of the melt at a shear rate of ec or higher, and more specifically, the shear stress τ(kvcrn
The log value of 1) is plotted on the vertical axis, and the shear speed r (aec-')
Plot the values using the log value of Logr as the horizontal axis, and α of Logr
This is the value found as .

If the difference in the structural viscosity index is smaller than the above range, the two resin layers will mix during co-injection, which will be described later, and a clearly differentiated ethylene-vinyl alcohol copolymer will appear in the preform. It becomes difficult to form a continuous and complete layer of coalescence. Furthermore, if the difference in structural viscosity index is larger than the above range, co-injection itself tends to become difficult.

The structural viscosity index of the melt depends on the molecular weight, molecular weight distribution and chemical structure of the resin. In the present invention, by selecting the molecular weight and molecular weight distribution of the polyester and ethylene-vinyl alcohol copolymer used, the difference in structural viscosity index can be set within the range described above.

Manufacturing Method In FIG. 2, which shows a co-injection apparatus used for manufacturing the multilayer 7-ohm multilayer resin of the present invention, a cavity 23 corresponding to a preform is formed between an injection mold 21 and a core mold 22. An f-toe 24 is located at a position corresponding to the bottom of the preform of the mold 21, and is connected to two injection machines 27 and 28 via a hot runner nozzle 25 and a hot runner block 26. The main injection machine 27 is for polyester injection, and is equipped with a sill 29 and a screen 30 inside it.The sub-injection machine 28 is for injection of ethylene-vinyl alcohol copolymer, and has a barrel 31 and The tee is provided with a screw 32 inside thereof. The block 26 and the nozzle 25 have a hot runner 33 with an annular cross section for injection of polyester, and a hot runner 34 for injection of ethylene vinyl alcohol copolymer located at the center of the hot runner 33, which are coaxial. Further, they are provided so as to merge near the tip of the nozzle 25. The sprue 35 for polyester injection is connected to a hot runner 33 via a sprue bush 36, while the sprue 37 for ethylene vinyl alcohol copolymer injection is connected to a hot runner 34 via a sprue bush 38. After melting the resin to be injected in the barrel 29.31 and storing it in the cylinder 29.31 by the rotation of the screw 30.32, it is ready! J, -30, 32 are advanced to inject the molten resin into the cavity 23 through the sprue 35, 37, the hot runners 33, 34 and the gate 24. According to the present invention, polyester and ethylene vinyl alcohol Injection of the copolymer is carried out under the following conditions.

In FIG. 3 showing the relationship between injection time and injection pressure of polyester and hyethylene-vinyl alcohol copolymer,
Alphabet symbols A-I in the figure are numbers 4-A to 4-
This corresponds to the explanatory diagram of FIG.

First of all? Advance the reester injection screen -30,
The primary injection is made into the cavity 23 under constant pressure. Fourth
Figure A shows the state of polyester just before injection, with polyester 40 at the tip of the nozzle 25, but ethylene-
The vinyl alcohol copolymer 41 remains at the tip of the hot runner 34. With the injection of polyester,
As shown in FIG. 4-B, the cavity 23 is partially filled with the primary injection polyester 40.

Step of injecting a predetermined amount of polyester, i.e. injection time 1. After the elapsed time, the screw 32 for injecting the ethylene-vinyl alcohol copolymer is advanced, and the cavity 2 is
Ethylene vinyl alcohol copolymer 41 is injected into the container. In this case, as shown in Figure 4-C, the cavity 2
In the surface area of No. 3, the injected polyester 40 is solidified upon contact with the mold, or even if it is not solidified, it is in a state of extremely high viscosity, and therefore the injected ethylene-vinyl Alcohol copolymer 41
flows toward the tip of the cavity along approximately the central plane of the filled polyester layer, forming an intermediate layer of the copolymer.

At time t2 when the injection of the ethylene-vinyl alcohol copolymer is completed, secondary injection of the remaining polyester is performed. FIG. 4-D shows the state at the end of injection of the ethylene vinyl alcohol copolymer, and FIG. 4-E shows the initial state after the secondary injection of polyester has been carried out into the cavity.

The secondary injection polyester 42 is shown in Figures 4-F and 4-G.
As shown in the figure, the flow flows between the polyester layer 40m on the outside of the cavity and the ethylene-vinyl alcohol copolymer layer 41, presses the ethylene-vinyl alcohol copolymer layer 41 toward the inside of the cavity, and While the secondary injection polyester 42 stretches the ethylene-vinyl alcohol copolymer layer toward the cavity tip, it also stretches the ethylene-vinyl alcohol copolymer layer 41 and the primary injection polyester outer layer 40a toward the cavity tip. move forward toward

The advancement of the secondary injection polyester 42 and the accompanying stretching of the ethylene-vinyl alcohol copolymer layer 41 are performed up to the vicinity of the tip of the cavity 23, as shown in Figure 4-H. At the stage, i.e. time t3, the fourth
As shown in Figure-I, the secondary injection polyester 42 reaches the cavity tip 44 and the injection cycle ends.

According to the present invention, the ester is secondarily injected between the outer surface layer of the second-injected polyester and the ethylene-vinyl alcohol copolymer layer, and this second injection causes the ethylene-vinyl alcohol to be applied to the 7-ohm tip. In addition, the intermediate layer of ethylene vinyl alcohol copolymer was made sufficiently thinner than the outer surface layer of the I-reester, and was biased toward the inner surface of the container wall than the center surface. It is possible to form a distributed structure, and it is also possible to completely confine the ethylene vinyl alcohol copolymer intermediate layer between the polyesters.

At this time, according to the present invention, the cooling rate of the injection mold 11,
The injection timing or speed of each resin is adjusted so that the thickness of the intermediate layer has the distribution described above. To explain this point, the intermediate layer resin 41 is injected at its own injection pressure and then at the injection pressure of the secondary injection polyester 42, -second injection, j?
It progresses between the inner and outer surfaces of the reester 40 toward the tip of the capity. Under conditions where the temperature of the intermediate layer resin 41 is high and its melt viscosity is low, the intermediate layer resin is spread thinly,
On the other hand, under the opposite conditions, the intermediate layer resin remains thick. To provide this distribution structure, for example, the intermediate layer resin may be maintained at a relatively high temperature near the nozzle 25, that is, at the bottom of the parison, and maintained at a relatively low temperature as it approaches the tip of the cavity, that is, the upper end of the t4 parison. Adjust the injection mold temperature. For this purpose, the temperature is adjusted so that the nozzle side of the mold cavity is relatively hot and the cavity side opposite the nozzle is relatively low temperature. Further, when the injection of the intermediate layer resin and the secondary injection of the polyester resin are performed slowly, the cooling effect on the intermediate layer resin tends to have a large gradient in the thickness distribution.

To obtain a distribution structure with a gradient in the thickness ratio of the intermediate layer specified in the present invention, the temperature (1,) on the nozzle side in the cavity of the injection mold should be set to 100°C≧tl-tz with respect to the temperature (t1) on the opposite side of the nozzle. ≧1℃, especially 60℃≧t]2≧30℃, and 1. is 30 to 100℃, especially 40 to 70℃
It is desirable that the range be within the range of .

In the present invention, when the primary injection pressure of polyester is P1, the injection pressure of ethylene vinyl alcohol copolymer is P2%, and the secondary injection pressure of polyester is P3, these pressure conditions can be changed considerably. discovered.

Generally speaking, it is advantageous for the injection pressure P2 of the ethylene-vinyl alcohol copolymer to be higher than the primary injection pressure Pl of the polyester in order to form the ethylene-vinyl alcohol copolymer as a complete continuous phase. On the other hand, the secondary injection pressure P3 of polyester is the primary injection pressure P3 of polyester.
It has been found that satisfactory results can be obtained even when the value is much lower than l. It is desirable that P1+P2 and P3 have the following relationship.

Pl = 60 to 80 kg/cm (gauge).

p, ==so to 110 kg/l:m (gauge) and a pressure of 1.2 to 1.8 times Pl.

P3 = 20 to 50 kg7cm2 (gauge) and p
, 0.3 to 0.8 times the pressure.

In addition, in the injection neutrality of p,) Pl mentioned above, it was observed that the polyester injection screw substantially stopped during injection of the ethylene-vinyl alcohol copolymer, so the ethylene-vinyl alcohol copolymer was f-)
It is confirmed that the injection is being carried out through the fourth injection, but it is of course possible to continue the primary injection of the polyester even when the ethylene-vinyl alcohol copolymer is injected. In Figures C and 4-D, ethylene-
It may be considered that injection of two layers of vinyl alcohol copolymer and polyester proceeds.

In the present invention, it was a particularly surprising new finding that the secondary injection of polyester proceeded smoothly with a lower pressure than the primary injection. The exact reason for this is unknown, but the secondary injection polyester passes through the molten resin with low resistance and the ethylene that comes into contact with the secondary injection polyester.
It is believed that the vinyl alcohol copolymer melt acts as a lubricant to facilitate the flow of the secondary injection polyester.

In the co-injection molding method used in the present invention, it is natural that the injection amount of the ethylene-vinyl alcohol copolymer is related to the thickness of the intermediate layer of the ethylene-vinyl alcohol copolymer, but the primary injection amount of the polyester It is related to the thickness of the inner surface layer, and the amount of secondary injection of polyester is closely related to the degree of deviation of the inner surface side from the center in the thickness direction of the preform of the intermediate layer of ethylene-vinyl alcohol copolymer.

In the present invention, what is the ethylene-vinyl alcohol copolymer intermediate layer? Since it is much thinner than the polyester outer surface layer, the cavity volume is v, the primary injection capacity of polyester is 1, and the secondary injection capacity of polyester is V.
2. If the injection capacity of the ethylene-vinyl alcohol copolymer is v3, it is generally desirable that v3 be 1 to 20 inches of V, especially 5 to 10 inches, and - the secondary injection capacity and the secondary injection capacity. The ratio V, :V, is 30 near 0 to 80:20, especially 50:50 to 70:30.
It is desirable that the volume ratio be as follows.

That is, when the value of v3 is smaller than the above range, it tends to be difficult to significantly improve the gas barrier properties of the container, and when the value of v3 is larger than the above range, the preform is stretched and blown. The disadvantages are that the properties deteriorate and the cost of the container increases. ■If the ratio of 1 is smaller than the above range, the fatal disadvantage of 2 may be that the ethylene-vinyl alcohol copolymer capriform is exposed to the surface, while on the other hand, if the ratio of vl is larger than the above range, This makes it difficult to spread the ethylene-vinyl alcohol copolymer as an intermediate layer over substantially most of the area of the preform.6 Manufacture of stretch-blown multilayer container The structure thus obtained is shown in Figure 4-I. The multilayer IJ foam is subjected to stretch blow molding. Prior to this stretch blow molding, the multilayer preform is first rolled at a temperature at which the ester can be stretched, generally from 80 to 135°C, particularly from 90 to 1
Maintain temperature at 25°C. This temperature control process involves supercooling the polyester layer of the multilayer preform so that it is maintained in a substantially non-crystalline state (amorphous state), and then using a heating mechanism known per se such as hot air, infrared heaters, and high-frequency dielectric heating. The multilayer preform can be heated to the above temperature, or the multilayer preform may be cooled or allowed to cool in the injection mold or within the mold until the temperature of the multilayer preform reaches the above temperature. It can also be done by

5 and 6 for explaining the stretch blow molding operation, a mandrel 46 is inserted into the mouth of the bottomed multilayer preform 1, and the mouth is inserted into a pair of split molds 47a.
, 47b. A vertically movable stretching rod 48 is provided coaxially with the mandrel 46, and between the stretching rod 48 and the mandrel 46 is an annular passage 49 for blowing fluid.
There is.

The tip 50 of the stretching rod 48 is applied to the inner side of the bottom of the preform 1 and the stretching rod 48 is moved downward to perform tensile stretching in multiple axial directions, and to draw the material into the preform 45 through the passage 49. Fluid is blown into the mold, and the fluid pressure causes the preform to expand and stretch within the mold.

The degree of stretching of the preform is sufficient to impart molecular orientation, which will be described in detail later, but for this purpose, the stretching ratio in the container axial direction must be 1.2 to 10 times, particularly 1.5 to 5.
It is desirable to double the amount.

The thickness of each layer is t^=0.1 at the thinnest part of the body.
It is preferable that it is within the range of 1.0 to 1.0 m ta = 0.02 to 0.7 m tc = 0.005 to 0.2.

It can be easily confirmed by the molecular orientation of the polyester layer, fluorescence polarization method, birefringence method, density method, etc., but it can be easily evaluated by the density method. Generally speaking, the density of polyester at 20°C in the thinnest southern part of the body is 1.34 to 1.39.
g/,', particularly within the range of 1,635 to 1,38 j;l/-, it can be said that molecular orientation has been effectively performed.

Applications of the Invention The container of the present invention has the above-mentioned excellent properties and is therefore useful as a container for food contents, especially a lightweight container that blocks the permeation of oxygen, carbon dioxide, or aromatic components, such as beer. , cola, cider, carbonated fruit juice drinks, carbonated alcoholic beverages, etc., it has the advantage of significantly less cardenation loss compared to known containers.

Example The invention is illustrated by the following example.

Example 1 A main injector is supplied with polyethylene (PET) having an intrinsic viscosity of 0.72, and an ethylene-vinyl alcohol copolymer (EVOH) with a vinyl alcohol content of 70 molti is supplied to a sub-extruder.

First, about 60 kg/c of molten PET is transferred to the main injection machine.
Primary injection is performed at a pressure of rn', and then, after a delay of about 1 second, an injection pressure higher than the primary injection pressure is applied to 80 to 120 kl?
E melted from the sub-injection machine with pressure controlled at /-
A predetermined amount of VOH is injected for approximately 0.9 seconds into an injection mold whose temperature is controlled so that the temperature of the cavity is approximately 10°C lower than that of the core, and finally the main injection machine is injected with a pressure lower than the secondary injection pressure. PET melted at a low injection pressure of about 30 VU'm2
A multilayer preform of two types and three layers with a thickness of 4fi was molded by secondary injection. The thickness of the intermediate layer of this multilayer preform was 0.02+mm at the bottom, 0.25+m at the center of the body, and 0.45m above the body.

This multilayer preform was heated to about 98° C. and biaxially stretched and blown to have a length of 2.3 times and a width of 3 times to form a shape having an internal volume of 1.0 OOCC. The thickness of the middle layer EVOH of this YN) is 0.015 m at the bottom and 0.035 m at the center of the body.
, 0.401 m above the body, and the middle layer EVOH was thinnest at the bottom and located on the inner layer side, and gradually became thicker as it moved to the body and shoulders, and was located on the outer layer side. In this Mettle, the intermediate layer EVOH is also highly stretched and oriented, and the in-plane orientation coefficients measured by polarized fluorescence are l = 2.5 and m = 2.8.
And the density of the PET layer of the body is 1.365 g/
cm3 and low peel strength (approx. 20, @/15 r
a width), the intermediate layer EVOH is completely encapsulated in the inner and outer PET layers, and is well oriented in the body and shoulders, and the shoulders are thick, so that no blistering occurs. Even in the easy shoulder area, 4 gas? There were no blisters even in a 6-week storage test at 38°C filled with Ryuum carbonated drinks, and the product had a good appearance and a height of 1.
There was no peeling between the eyebrows and no damage to the bottom part due to the impact of dropping from m to floor l. Also, the oxygen permeability of this /) room is 37°C and the inside of the /) room is 100% RH.

2.4 cc/m224 H under external 20%RH condition,
A tm of polyethylene terephthalate alone with the same weight and shape has an oxygen permeability of 9.8 cc/
m2・24)(・latm, and the oxygen permeability of &tor of the present invention was about A compared to yl?tor of PET alone.

Comparative example An extruder for outer layer and an extruder for inner layer that have a built-in full-flight screw with a diameter of 65 mm and an effective length of 1.430 Tm.A built-in full-flight screw with a diameter of 50 m and an effective length of 1.100 Tm. Using an extruder for the intermediate layer and a ring-shaped die for the three layers, the inner layer and outer layer had an intrinsic viscosity of 0.7.
5 polyethylene terephthalate, the middle layer is made of vinyl alcohol-containing ethylene-vinyl alcohol copolymer with i60 mole, the thickness ratio of each layer is outer layer: middle layer: inner layer is IOO: 20:50, outer diameter 30.0 W 1 thickness 3 .8
The tube was coextruded using two extruders, passed through a multilayer die, and extruded into a water-cooled cooling tank to obtain a 2flt, 3-layer multilayer pipe. The thickness ratio of the intermediate layer of this pipe was approximately the same over the entire length. Using the obtained i4 tube, the lower end was fused and closed to form a semicircular sphere, and the upper end was formed into a mouth with a threaded part.The preform was preheated to 98°C and blown. Multi-layer stretching with internal volume of 1.0OOCC by biaxial stretching blow molding in the molding mold? I got Tor.

The thickness of the intermediate EVOH layer of this bottle is 0.25 a, o, o 5 m and 0 at the bottom, center of the body and above the body.
．． At 15m5+, the intermediate layer EVOH was exposed at the mouth end face and the bottom pinch-off part.

When this YN) was subjected to the same test as in Example 1, the delamination strength was as low as about 20, li'/1.5, and width, and blisters occurred on the shoulders, damaging the product value. At the same time, the pinch-off part at the bottom was damaged due to the impact and fall.

[Brief explanation of drawings]

Fig. 1 is a preform according to the present invention, Fig. 2 is a sectional view of essential parts of a co-injection molding machine, Fig. 3 is a chart showing the relationship between injection time and injection pressure, and Figs. 4-A to 4-1. The figure is an explanatory view showing the injection process, and FIGS. 5 and 6 are sectional views of essential parts of the stretch blow molding machine. 1... Glyphome, 2... Mouth, 3... Torso,
4...Bottom, bottom...Chee, side, 1o...Inner surface layer, 11...Middle layer, 12...Outer surface layer, 21...
・Injection mold, 22... Core mold, 27.28... Injection machine, 33.34... Hot runner-14o... Polyester, 41... Ethylene-vinyl alcohol co'tlUr body, 47 a. 47b...Blow mold. Figure 1 Figure 2 Figure 3 Figure 4-G Figure 4-H Figure 4-I Figure 5 Figure 6

Claims (1)

[Claims] (1) A stretch blow molding preform consisting of a mouth part, a cylindrical body part, and a closed bottom part formed from a multilayer plastic, and the preform has an inner and outer surface layer of an oriented, creep-resistant resin and an inner and outer surface layer of the polyester layer. an intermediate layer of a gas-barrier thermoplastic resin completely encapsulated in a gas-barrier thermoplastic resin, the intermediate layer having a thickness distribution such that it is thinnest at the bottom and becomes thicker from the lower part of the body to the upper part of the body; The thickness of the middle layer above the trunk (t_1) is the thickness of the middle layer at the bottom (t_
A preform characterized by having a thickness 1.1 to 25 times that of 1).